It conveys more than "don't judge a book by its cover." It is making the stronger point that not only are people who are unkempt in their appearance just as lik

It conveys more than "don't judge a book by its cover." It is making the stronger point that not only are people who are unkempt in their appearance just as likely to be good at their job, they're more likely to be good at their job. He explains a model that this prediction falls out of: where there is competition between professionals and they can either get their status through expertise, superficial preening, or some combination thereof. Most people think those two traits go hand in hand but he's making the point that due to competition they might be anti-correlated.